chapter 3 studio acoustics francis group and design

The Audio Cyclopedia defines acoustics as “a science dealing with the production,effects and transmission of sound waves; the transmission of sound wavesthrough various mediums, including reflection, refraction, diffraction, absorptionand interference; the characteristics of auditoriums, theaters and studios, as wellas their design.” We can see from this description that the proper acousticdesign of music recording, project and audio-for-visual or broadcast studios isoften no simple matter. A wide range of complex variables and interrelationshipsoften come into play in the creation of a successful acoustic and monitoringdesign. When designing or redesigning an acoustic space, the following basicrequirements should be considered:

n Acoustic isolation: This prevents external noises from transmitting into thestudio environment through the air, ground or building structure. It canalso prevent feuds that can arise when excessive volume levels leak outinto the surrounding neighborhood.

n Frequency balance: The frequency components of a room shouldn’t adverselyaffect the acoustic balance of instruments and/or speakers. Simply stated,the acoustic environment shouldn’t alter the sound quality of the originalor recorded performance.

n Acoustic separation: The acoustic environment should not interfere withintelligibility and should offer the highest possible degree of acousticseparation within the room (often a requirement for ensuring that soundsfrom one instrument aren’t unduly picked up by another instrument’smicrophone).

n Reverberation: The control of sonic reflections within a space is an importantfactor for maximizing the intelligibility of music and speech. No matterhow short the early reflections and reverb times are, they will add an im -portant psychoacoustic sense of “space” in the sense that they can giveour brain subconscious cues as to a room’s size, number of reflectivebound aries, distance between the source and listener, and so forth.

n Cost factors: Not the least of all design and construction factors is cost. Multi -million-dollar facilities often employ studio designers and construction

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CHAPTER 3

Studio Acoustics and Design

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Studio Acoustics and Design

teams to create a plush decor that’s been acoustically tuned to fit the needsof both the owners and their clients. Owners of project studios and budget-minded production facilities, however, can all take full advantage of thesame basic acoustic principles and construction techniques and apply themin cost-effective ways.

This chapter will discuss many of the basic acoustic principles and constructiontechniques that should be considered in the design of a music or soundproduction facility. I’d like to emphasize that any or all of these acoustical topicscan be applied to any type of audio production facility and aren’t only limitedto professional music studio designs. For example, owners of modest projectand bedroom studios should know the importance of designing a control roomthat’s symmetrical and hopefully feels and sounds good. It doesn’t cost anythingto know that if one speaker is in a corner and the other is on a wall, the perceivedcenter image and frequency balance will be screwy. As with many techno-artisticendeavors, studio acoustics and design are a mixture of fundamental physics(in this case, mostly dimensional mathematics) with an equally large dose ofcommon sense and dumb luck. More often than not, acoustics is an artisticscience that melds physics with the art of intuition and experience.

STUDIO TYPESAlthough the acoustical fundamentals are the same for most studio designtypes, differences will often follow the form, function and budgets required bythe tasks at hand. Some of the more common studio types include:

n Professional music studios

n Audio-for-visual production environments

n Audio-for-gaming production environments

n Project studios

The Professional Recording StudioThe professional recording studio (Figure 3.1) is first and foremost a commercialbusiness, so its design, decor and acoustical construction requirements are oftenmuch more demanding than those of a privately owned project studio. In somecases, an acoustical designer and experienced construction team are placed incharge of the overall building phase of a professional facility. In others, thestudio’s budget is just too tight to hire such professionals, which places thestudio owners and staff squarely in charge of designing and constructing theentire facility. Whether you happen to have the luxury of building a new facilityfrom the ground up or are renovating a studio within an existing shell, youcould easily benefit from a professional studio designer’s experience and skills.Such expert advice sometimes proves to be cost effective in the long run, becauseerrors in design judgment can lead to cost overruns, lost business due tounexpected delays or the unfortunate state of living with mistakes that couldhave been avoided.

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77Studio Acoustics and Design CHAPTER 3

The Audio-for-Visual Production EnvironmentAn audio-for-visual production facility is used for video, film post-production(often simply called “post”) and includes such facets as music recording forfilm or other media (scoring), score mixdown, automatic dialog replacement(ADR—the replacement of on- and off-screen dialog to visual media) and Foley (the replacement and creation of on- and off-screen sound effects). Aswith music studios, audio-for-visual production facilities can range from high-end facilities that can accommodate the posting needs of network video orfeature film productions (Figure 3.2) to a simple, budget-minded project studiothat’s equipped with video and a digital audio work station. As with the musicstudio, audio-for-visual construction and design techniques often span a widerange of styles and scope in order to fit the budget needs at hand.

The Audio-for-Gaming Production EnvironmentWith the ever-increasing popularity of having the gaming experience in the home,budgets and the need for improved audio in newer game releases, productionfacilities have sprung up that deal exclusively with the recording and post-production aspects of game audio. These can range from high-end facilities thatresemble the high-end music studio, to production houses that deal with the

FIGURE 3.1 Professional studioexamples. (a) BiCoastalMusic, Ossining, NY.(Courtesy of Russ BergerDesign Group, www.rbdg.com) (b) London BridgeStudios big tracking room,Seattle. (Courtesy of LondonBridge Studios,www.londonbridgestudio.com, Photo by ChristopherNelson)

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Studio Types78

day-to-day creation and programming of the hundreds of thousands of audioclips that go into a modern game. Although the production needs of audio-for-gaming is quite different from music production, the required skills and needfor attention to technical detail demand a high level of skill and dedication, asa single production schedule can easily last for several months.

The Project StudioIt goes without saying that the vast majority of audio production studios fallinto the project studio category. This basic definition of such a facility is opento interpretation. It’s usually intended as a personal production resource forrecording music, audio-for-visual production, multimedia production, voice -overs—you name it. Project studios can range from being fully commercial innature to smaller setups that are both personal and private (Figure 3.3). All ofthese possible studio types have been designed with the idea of giving artiststhe flexibility of making their art in a personal, off-the-clock environment that’sboth cost and time effective. Of course, the design and construction consid -erations for creating a privately owned project studio will often differ from thedesign considerations for a professional music facility in two fundamental ways:

n Building constraints

n Cost

FIGURE 3.2 Radiobu audio productionand post facility. (Courtesyof Russ Berger DesignGroup, Inc., www.rbdg.com)

FIGURE 3.3 Gettin’ it all going in theproject studio. (a) Courtesyof Yamaha Corporation ofAmerica,www.yamaha.com. (b) Courtesy of UniversalAudio, www.uaudio.com© 2017 Universal Audio,Inc. All rights reserved.Used with permission.

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Generally, a project studio’s room (or series of rooms) is built into an artist’shome or a rented space where the construction and dimensional details arealready defined. This fact (combined with inherent cost considerations) oftenleads the owner/artist to employ cost-effective techniques for sonically treatingany deficiencies within the room. Even if the room has little or no treatment,keep in mind that a basic knowledge of acoustical physics and room design canbe a valuable and cost-effective tool, as your experience, production needs andbusiness abilities grow.

Modern-day digital audio workstations (DAWs) have squarely placed the Macand PC in the middle of almost every pro and home project studio (Figure 3.4).In fact, in many cases, the DAW is the project studio. With the advent of self-powered speaker monitors, cost-effective microphones and hardware DAWcontrollers, it’s a relatively simple matter to design a powerful production systeminto almost any existing space.


FIGURE 3.4 Mark Needham’s productionroom which centers aroundtwo Raven MTX touchscreen controllers.(Courtesy of Slate Pro Audio,www.slateproaudio.com)

PRIMARY FACTORS GOVERNING STUDIO AND CONTROL ROOM ACOUSTICSRegardless of which type of studio facility is being designed, built and used, anumber of primary concerns should be addressed in order to achieve the bestpossible acoustic results. In this section, we’ll take a close look at such importantand relevant aspects of acoustics as:

n Acoustic isolation

n Symmetry in control room and monitoring design

n Frequency balance

n Absorption

n Reflection

n Reverberation

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Primary Factors80

Although several mathematical formulas have been

included in the following sections, it’s by no means

necessary that you memorize or worry about them.

By far, I feel that it’s more important that you grasp

the basic principles of acoustics rather than worry

about the underlying math. Remember: More often

than not, acoustics is an artistic science that blends

math with the art of intuition and experience.

Acoustic IsolationBecause most commercial and project studio environments make use of anacoustic space to record sound, it’s often wise and necessary to employ effectiveisolation techniques into their design in order to keep external noises to aminimum. Whether that noise is transmitted through the medium of air (e.g.,from nearby auto, train or jet traffic) or through solids (e.g., from air-conditionerrumbling, underground subways or nearby businesses), special constructiontechniques will often be required to dampen these extraneous sounds (Figure 3.5).

FIGURE 3.5 Various isolation, absorptionand reflective acousticaltreatments for theconstruction of arecording/monitoringenvironment. (Courtesy ofAuralex Acoustics,www.auralex.com)

If you happen to have the luxury of building a studio facility from the groundup, a great deal of thought should be put into selecting the studio’s location.If a location has considerable neighborhood noise, you might have to resort toextensive (and expensive) construction techniques that can “float” the rooms(a process that effectively isolates and decouples the inner rooms from thebuilding’s outer foundations). If there’s absolutely no choice of studio locationand the studio happens to be located next to a recycling factory, just under the airport’s main landing path or over the subway’s uptown line you’ll simplyhave to give in to destiny and build acoustical barriers to these outsideinterferences.

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The reduction in the sound-pressure level (SPL) of a sound source as it passesthrough an acoustic barrier of a certain physical mass (Figure 3.6) is termed thetransmission loss (TL) of a signal. This attenuation can be expressed (in dB) as:

TL = 14.5 log M + 23

where TL is the transmission loss in decibels, and M is the surface density (orcombined surface densities) of a barrier in pounds per square foot (lb/ft2).

FIGURE 3.6 Transmission loss refers tothe reduction of a soundsignal (in dB) as it passesthrough an acoustic barrier.

Because transmission loss is frequency dependent, the following equation canbe used to calculate transmission loss at various frequencies with some degreeof accuracy:

TL = 14.5 log Mf – 16

where f is the frequency (in hertz).

Both common sense and the preceding two equations tell us that heavier acousticbarriers will yield a higher transmission loss. For example, Table 3.1 tells usthat a 12-inch-thick wall of dense concrete (yielding a surface density of 150lb/ft2) offers a much greater resistance to the transmission of sound than cana 4-inch cavity filled with sand (which yields a surface density of 32.3 lb/ft2).From the second equation (TL = 14.5 log Mf – 16), we can also draw the con -clusion that, for a given acoustic barrier, transmission losses will increase as thefrequency rises. This can be easily illustrated by closing the door of a car thathas its sound system turned up, or by shutting a single door to a music studio’scontrol room. In both instances, the high frequencies will be greatly reducedin level, while the bass frequencies will be impeded to a much lesser extent.From this, the goal would seem to be to build a studio wall, floor, ceiling,window or door out of the thickest and most dense material that’s available;however, expense and physical space often play roles in determining just howmuch of a barrier can be built to achieve the desired isolation. As such, a balancemust usually be struck when using both space- and cost-effective buildingmaterials. Co

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Primary Factors82

WALLS

When building a studio wall or reinforcing an existing structure, the primarygoal is to reduce leakage (increase the transmission loss) through a wall as muchas possible over the audible frequency range. This is generally done by:

n Building a wall structure that’s as massive as is practically possible (bothin terms of cubic and square foot density)

n Eliminating joints that can easily transmit sound through the barrier

n Dampening structures, so that they are well supported by reinforcementstructures and are free of resonances

The following guidelines can be helpful in the construction of framed wallsthat have high transmission losses:

n If at all possible, the inner and outer wallboards should not be directlyattached to the same wall studs. The best way to avoid this is to alternatelystagger the studs along the floor and ceiling frame (i.e., framing 2 × 4 studs

Material Thickness Surface Density(inches) (lb/ft2)

Brick 4 40.0

8 80.0

Concrete (lightweight) 4 33.0

12 100.0

Concrete (dense) 4 50.0

12 150.0

Glass — 3.8

— 7.5

— 11.3

Gypsum wallboard — 2.1

— 2.6

Lead 1/16 3.6

Particleboard — 1.7

Plywood — 2.3

Sand 1 8.1

4 32.3

Steel — 10.0

Wood 1 2.4

Table 3.1 Surface Densities of Common Building Materials

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onto a 2 × 6 frame), so that the front/back facing walls aren’t in physicalcontact with each other (Figure 3.7).

n Each wall layer should have a different density to reduce the likelihoodof increased transmission due to resonant frequencies that might besympathetic to both sides. For example, one wall might be constructed oftwo 5/8-inch gypsum wallboards, while the other wall might beunderplayed with soft fiberboard that’s also surfaced with two 3/4-inchgypsum wallboards.

n If you’re going to attach gypsum wallboards to a single wall face, you canincrease transmission loss by mounting the additional layers (not the firstlayer) with adhesive caulking rather than by using screws or nails.

n Spacing the studs 24 inches on center instead of using the traditional 16-inch spacing yields a slight increase in transmission loss.

n To reduce leakage that might make it through the cracks, apply a bead ofnon-hardening caulk sealant to the inner gypsum wallboard layer at thewall-to-floor, wall-to-ceiling and corner junctions.

Generally, the same amount of isolation is required between the studio and thecontrol room as is required between the studio’s interior and exterior environ -ments. The proper building of this wall is important, so that an accurate tonalbalance can be heard over the control-room monitors without promoting leakagebetween the rooms or producing resonances within the wall that would audiblycolor the signal. Optionally, a specially designed cavity, called a soffit, can bedesigned into the front-facing wall of the control room to house the larger studiomonitors. This superstructure allows the main, far field studio monitors to bemounted directly into the wall to reduce reflections and resonances in themonitoring environment.

It’s important for a soffit to be constructed to high standards, using a multiple-wall or high-mass design that maximizes the density with acoustically tightconstruction techniques in order to reduce leakage between the two rooms.Cutting corners by using substandard (and even standard) constructiontechniques in the building of a studio soffit can lead to unfortunate side effects,such as wall resonances, rattles, and increased leakage. Typical wall constructionmaterials include:


FIGURE 3.7 Double, staggered studconstruction greatly reducesleakage by decoupling thetwo wall surfaces from eachother: (a) top view showingwalls that are directly tied towall studs (allowing soundto easily pass through); (b) top view showing wallswith offset, non-touchingstuds (so that sound doesn’teasily pass from wall towall).

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Primary Factors

n Concrete: This is the best and most solid material, but it is often expensiveand it’s not always possible to pour cement into an existing design.

n Bricks (hollow-form or solid): This excellent material is often easier to placeinto an existing room than concrete.

n Gypsum plasterboard: Building multiple layers of plasterboard onto a double-walled stud frame is often the most cost- and design-efficient approachfor reducing resonances and maximizing transmission loss. It’s often agood idea to reduce these resonances by filling the wall cavities withRockwool or fiberglass, while bracing the internal structure to add an extradegree of stiffness.

Studio monitors can be designed into the soffit in a number of ways. In oneexpensive approach, the far-field speakers’ inner enclosure cavities are literallythe walls of the control room’s front wall concrete pour. Under these conditions,resonances are completely eliminated. Another less expensive approach has thestudio monitors resting on poured concrete pedestals; in this situation, insertscan be cast into the pedestals that can accept threaded rebar rods (known asall-thread). By filing the rods to a chamfer (a sharp point), it’s possible to adjustthe position, slant and height of the monitors for final positioning into thesoffit’s wall framing. The most common and affordable approach uses traditionalwood framing in order to design a cavity into which the speaker enclosures canbe designed and positioned. Extra bracing, plasterboard and heavy constructionshould be used to reduce resonances.

FLOORS

For many recording facilities, the isolation of floor-borne noises from roomand building exteriors is an important consideration. For example, a buildingthat’s located on a busy street and whose concrete floor is tied to the building’sground foundation might experience severe low-frequency rumble from nearbytraffic. Alternatively, a second-floor facility might experience undue leakagefrom a noisy downstairs neighbor or, more likely, might interfere with a quieterneighbor’s business. In each of these situations, increasing the isolation toreduce floor-borne leakage and/or transmission is essential. One of the mostcommon ways to isolate floor-related noise is to construct a “floating” floorthat’s structurally decoupled from its subfloor foundation.

Common construction methods for floating a professional facility’s floor useseither neoprene “hockey puck” isolation mounts, U-Boat floor floaters (Figure3.8a), or a continuous underlay, such as a rubberized floor mat. In these cases,the underlay is spread over the existing floor foundation and then covered withan overlaid plywood floor structure. In more extreme situations, this super -structure could be covered with reinforcing wire mesh and finally topped witha 4-inch layer of concrete (Figure 3.8b). In either case, the isolated floor is thenready for carpeting, wood finishing, painting or any other desired surface.

An even more cost- and space-effective way to decouple a floor involves layeringthe original floor with a rubberized or carpet foam pad. A 1/2- or 5/8-inch layer

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of tongue-and-groove plywood or oriented strand board (OSB) is then laid ontop of the pad. These should not be nailed to the subfloor; instead, they canbe stabilized by glue or by locking the pieces together with thin, metal braces.Another foam pad can then be laid over this structure and topped with carpetingor any other desired finishing material (Figure 3.9).

It is important that the floating superstructure be isolated from both the under-flooring and the outer wall. Failing to isolate these structures allows sounds tobe transmitted through the walls to the subfloor, and vice versa (often defeatingthe whole purpose of floating the floor). These wall perimeter isolation gapscan be sealed with pliable decoupling materials such as widths of soft mineralfiberboard, neoprene, silicone or other pliable materials.

Caulk this small gap at each layer

1/2” or 5/8” Particle Board5/8” Drywall

3/4” Particle Board

Glue these layers together & screw them to the framing members

Insulate this cavity

Framing member(2x4 shown)

U-Boat (Duh)

Existing wall SheetBlok

4” concrete

reinforcing mesh

plastic sheet 6 mil

marine plywood 1/2”

neoprene or fiberglassmounts

perimiterisolation

board

(a) (b)

FIGURE 3.8 Floor isolation treatments.(a) U-Boat™ floor beamfloat channels can be placedunder a standard 2x4 floorframe to increase isolation.Floor floaters should beplaced every 16 inchesunder a 2x4 floor joist.(Courtesy of AuralexAcoustics, www.auralex.com) (b) Basic guidelines forbuilding a concrete floatingfloor using neoprenemounts.

FIGURE 3.9 An alternative, cost-effective way to float anexisting floor is by layeringrelatively inexpensivematerials.

RISERS

As we saw from the equation TL = 14.5 log Mf – 16, low-frequency sound travelsthrough barriers much more easily than does high-frequency sound. It standsto reason that strong, low-frequency energy is transmitted more easily than high-frequency energy between studio rooms, from the studio to the control room

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Primary Factors86

or to outside locations. In general, the drum set is most likely to be the biggestleakage offender. By decoupling much of a drum set’s low-frequency energyfrom a studio floor, many of the low-frequency leakage problems can be reduced.In most cases, the problem can be fixed by using a drum riser. Drum risers areavailable commercially (Figure 3.10a), or they can be easily constructed. In order to reduce unwanted resonances, drum risers should be constructed using 2 × 6-inch or 2 × 8-inch beams for both the frame and the supportingjoists (spaced at 16 or 12 inches on center, as shown in Figure 3.10b). Sturdy1/2- or 5/8-inch tongue-and-groove plywood panels should be glued to thesupporting frames with carpenter’s glue (or similar wood glue) and then nailedor screwed down (using heavy-duty, galvanized fasteners). When the frame hasdried, rubber coaster float channels or (at the very least) strips of carpeting shouldbe attached to the bottom of the frame, and the riser will be ready for action.

CEILINGS

Foot traffic and other noises from above a sound studio or production roomare another common source of external leakage. Ceiling noise can be isolatedin a number of ways. If foot traffic is your problem and you’re fortunate enoughto own the floors above you, you can reduce this noise by simply carpeting theoverhead hallway or by floating the upper floor. If you don’t have that luxury,one approach to isolating ceiling-borne sounds is to hang a false structure fromthe existing ceiling or from the overhead joists (as is often done when a newroom is being constructed). This technique can be fairly cost effective when

FIGURE 3.10 Drum/isolation risers. (a) HoverDeckTM 88 isolationriser. (Courtesy of AuralexAcoustics, www.auralex.com) (b) Generalconstruction details for ahomemade drum riser.

FIGURE 3.11 Ceiling isolator systems. (a) RSICSI-1 (ResilientSound Isolation Clips).(Courtesy of PACInternational, Inc; www.pac-intl.com) (b) Z channelscan be used to hang afloating ceiling from anexisting overhead structure.

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spring or “Z” suspension channels are used (Figure 3.11). Z channels are oftenscrewed to the ceiling joists to provide a flexible, yet strong support to whicha hanging wallboard ceiling can be attached. If necessary, fiberglass or othersound-deadening materials can be placed into the cavities between the overheadstructures.

WINDOWS AND DOORS

Access to and from a studio or production room area (in the form of windowsand doors) can also be a potential source of sound leakage. For this reason,strict attention needs to be given to window and door design and construction.Visibility in a studio is extremely important within a music production environ -ment. For example, when multiple rooms are involved, good visibility servesto promote effective communication between the producer or engineer and thestudio musician (as well as among the musicians themselves). For this reason,windows have been an important factor in studio design since the beginning.The design and construction details for a window often vary with studio needsand budget requirements and can range from being deep, double-plate cavitiesthat are built into double-wall constructions (Figure 3.12) to more modest prefabdesigns that are built into a single wall. Other more expensive designs includefloor-to-ceiling windows that create a virtual “glass wall,” as well as thoseimpressive ones which are designed into poured concrete soffit walls.


FIGURE 3.12 Detail for a practical windowconstruction between thecontrol room and studio. (a) Simplified drawing. (b) Detailed drawing.(Courtesy of Russ BergerDesign Group, Inc.,www.rbdg.com)

Access doors to and from the studio, control room, and exterior areas shouldbe constructed of solid wood or high-quality acoustical materials (Figure 3.13a),as solid doors generally offer higher TL values than their cheaper, hollowcounterparts. No matter which door type is used, the appropriate seals, weatherstripping, and doorjambs should be used throughout so as to reduce leakagethrough the cracks. Whenever possible, double-door designs should be used to

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Primary Factors88

form an acoustical sound lock (Figure 3.13b). This construction techniquedramatically reduces leakage because the air trapped between the two solidbarriers offers up high TL values.

ISO-ROOMS AND ISO-BOOTHS

Isolation rooms (iso-rooms) are acoustically isolated or sealed areas that are builtinto a music studio or just off of a control room (Figure 3.14). These recordingareas can be used to separate louder instruments from softer ones (and viceversa) in order to reduce leakage and to separate instrument types by volumeto maintain control over the overall ensemble balance. For example:

n To eliminate leakage when recording scratch vocals (a guide vocal trackthat’s laid down as a session reference), a vocalist might be placed in asmall room while the rhythm ensemble is placed in the larger studio area.

n A piano or other instrument could be isolated from the larger area that’shousing a full string ensemble.

n Vocals could be set up in the iso-room, while drums are being laid downin the main room. The possibilities are endless.

An iso-room can be designed to have any number of acoustical properties. Byhaving multiple rooms and/or iso-room designs in a studio, several acousticalenvironments can be offered that range from being more reflective (live) to

FIGURE 3.13 Door isolation systems. (a) A SoundSecureTM studiodoor. (Courtesy of ETS-Lindgren, www.ets-lindgren.com) (b) Exampleof a sound lock door systemdesign.

FIGURE 3.14 Studio incorporatingmultiple iso-rooms.(Courtesy of Blade Studios,www.bladestudios.com) Co

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absorptive (dead), or a specific room can be designed to better fit the acousticalneeds of a particular instrument (e.g., drums, piano or vocals). These roomscan be designed as totally separate areas that can be accessed from the mainstudio or control room, or they might be directly tied to the main studio byway of sliding walls or glass sliding doors. In short, their form and functioncan be put to use to fit the needs and personality of the session.

Isolation booths (iso-booths) provide the same type of isolation as an iso-room,but are often much smaller. Often called vocal booths, these mini-studios areperfect for isolating vocals and single instruments from the larger studio. Infact, rooms that have been designed and built for the express purpose of mixingdown a recording will often only have an iso-booth . . . and no other recordingroom. Using this space-saving option, vocals or single instruments can be easilyoverdubbed on site, and should more space be needed a larger studio can bebooked to fit the bill.

ACOUSTIC PARTITIONS

Movable acoustic partitions (also known as flats or gobos) are commonly usedin studios to provide on-the-spot barriers to sound leakage. By partitioning amusician and/or instrument on one or more sides and then placing the micinside the temporary enclosure, isolation can be greatly improved in a flexibleway that can be easily changed as new situations arise. Acoustic partitions arecurrently available on the commercial market in various design styles and typesfor use in a wide range of studio applications (Figure 3.15). For those on abudget, or who have particular isolation needs, it’s relatively simple to get outthe workshop tools and make your own flats that are based around woodframes, fiberglass, Rockwool or other acoustically absorptive materials—and thendecorate them with your favorite fabric coverings (Figure 3.16a).

If you can’t get a flat when you need one, you can often improvise usingcommon studio and household items. For example, a simple partition can beeasily made on the spot by grabbing a mic/boom stand combination andretracting the boom halfway at a 90º angle to make a T-shape. Simply drape a


FIGURE 3.15 Acoustic partition flatexamples: (a) S5–2L“Sorber” baffle system.(Courtesy of ClearSonicMfg., Inc., www.clearsonic.com); (b) piano panel setup.(Courtesy of AuralexAcoustics, www.auralex.com)

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Primary Factors90

blanket or heavy coat over the T-bar and voilà—you’ve built a quick-’n’-dirtydividing flat (Figure 3.16b).

When using a partition, it’s important to be aware that musicians need to beable to see each other, the conductor and the producer. Musicality and humanconnectivity almost always take precedence over technical issues.

NOISE ISOLATION WITHIN THE CONTROL ROOM

Isolation between rooms and the great outdoors isn’t the only noise-relatedissue in the modern-day recording or project studio. The proliferation ofcomputers, multitrack tape machines and cooling systems has created issuesthat present their own Grinch-like types of noise, Noise, NOISE! This usuallymanifests itself in the form of system fan noise, transport tape noise andcomputer-related sounds from CPUs, case fans, hard drives and the like.

When it comes to isolating tape transport and system fan sounds, budget andsize constraints permitting, it’s often wise to build an iso-machine room or iso-closet that’s been specifically designed and ventilated for containing suchequipment. An equipment room that has easy-access doors that provide forcurrent/future wiring needs can add a degree of peace-’n’-quiet and an overallprofessionalism that will make both you and your clients happy.

Within smaller studio or project studio spaces, such a room isn’t always possible,however, with care and forethought the whizzes and whirrs of the digital eracan be turned into a non-issue that you’ll be proud of. Here are a few examplesof the most common problems and their solutions:

n Place the computer(s) in an isolated case, alcove or room (care needs tobe taken to provide ventilation and to monitor the CPU/case temperaturesso as not to harm your system).

n Connect the studio computers via a high-speed network to a remote serverlocation.

n Replace fans with quieter ones. By doing some careful Web searching orby talking to your favorite computer salesperson, it’s often possible toinstall CPU and case fans that are quieter than most off-the-shelf models.

FIGURE 3.16 Examples of a homemadeflat: (a) homemade flatdesign; (b) the old “blanketand a boom” trick.

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Symmetry in Control Room DesignWhile many professional studios are built from the ground up using standardacoustic and architectural guidelines, most budget-minded production andproject studios are often limited by their own unique sets of building, spaceand acoustic constraints. Even though the design of a budget, project or bedroomcontrol room might not be acoustically perfect, if speakers are to be used in themonitoring environment, certain ground rules of acoustical physics must befollowed in order to create a proper listening environment.

One of the most important acoustic design rules in a monitoring environmentis the need for symmetrical reflections on all axes within the design of a controlroom or single-room project studio. In short, the center and acoustic imaging(ability to discriminate placement and balance in a stereo or surround field) isbest when the listener, speakers, walls and other acoustical boundaries are sym -metrically centered about the listener’s position (often in an equilateral triangle).In a rectangular room, the best low-end response can be obtained by orientingthe console and loudspeakers into the room’s long dimension (Figure 3.17a).Should space or other room considerations come into play, centering thelistener/monitoring position at a 45º angle within a symmetrical corner (Figure3.17b) is another example of how the left/right imagery can be reasonablymaintained.

FIGURE 3.17 Various acceptablesymmetries in a monitoringenvironment. (a) Acousticreflections must besymmetrical about thelistener’s position. Inaddition, orienting a controlroom along the longdimension can extend theroom’s low-end response.(b) Placing the listeningenvironment symmetricallyin a corner is anotherexample of how theleft/right imagery can beimproved over an off-centerplacement.

With regard to setting up any production/monitoring

environment, I’d like to first draw your attention to

the need for symmetry in any critical monitoring

environment. A symmetrical acoustic environment

around the central mixing axis can work wonders

toward creating a balanced left/right and surround

image. Fortunately, this generally isn’t a difficult goal

to achieve. An acoustical and speaker placement

environment that isn’t balanced between the left-

hand and right-hand sides will allow for differing

reflections, absorption coefficients and variations in

frequency response. This can adversely affect the

imaging and balance of your final mix. Further

information on this important subject can be found

later in this chapter, however, consider this your first

heads-up on an important topic.

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Primary Factors92

While we’re on the subject of the relationship between the room’s acoustic layoutand speaker placement, it’s always wise to place near-field and all other speakerenclosures at points that are equidistant to the listener in the stereo and surroundfield. Whenever possible, speaker enclosures should be placed 1 to 2 feet awayfrom the nearest wall and/or corner, which helps to avoid bass buildups thatacoustically occur at boundary and corner locations. In addition to strategicspeaker placement, homemade or commercially available isolation pads can beused to reduce resonances that often occur whenever enclosures are placeddirectly onto a table or flat surface.

Frequency BalanceAnother important factor in room design is the need for maintaining the originalfrequency balance of an acoustic signal. In other words, the room should exhibita relatively flat frequency response over the entire audio range without addingits own particular sound coloration. The most common way to control the tonalcharacter of a room is to use materials and design techniques that govern theacoustical reflection and absorption factors.

FIGURE 3.18 Center symmetry. (a) Placing the monitoringenvironment off-center andin a corner will affect theaudible center image, andplacing one speaker in a90º corner can cause an off-center bass buildup andadversely affect the mix’simagery. (b) Shifting thelistener/monitoring positioninto the center will greatlyimprove the left/rightimagery.

Should any primary boundaries of a control room (especially wall or ceilingboundaries near the mixing position) be asymmetrical from side to side, soundsheard by one ear will receive one combination of direct and reflected sounds,while the other ear will hear a different acoustic balance (Figure 3.18). Thiscondition can drastically alter the sound’s center image characteristics, so thatwhen a sound is actually panned between the two monitor speakers the soundwill appear to be centered; however, when the sound is heard in another studioor standard listening environment the imaging may be off center. To avoid thisproblem, care should be taken to ensure that both the side and ceiling bound -aries are largely symmetrical with respect to each other and that all of the speakerlevel balances are properly set.

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REFLECTIONS

One of the most important characteristics of sound as it travels through air isits ability to reflect off a boundary’s surface at an angle that’s equal to (andopposite of) its original angle of incidence (Figure 3.19). Just as light bouncesoff a mirrored surface or multiple reflections can appear within a mirrored room,sound reflects throughout room surfaces in ways that are often amazinglycomplex. Through careful control of these reflections, a room can be altered toimprove its frequency response and sonic character.

FIGURE 3.19 Sound reflects off a surfaceat an angle equal (andopposite) to its originalangle of incidence, much aslight will reflect off a mirror.

In Chapter 2, we learned that sonic reflections can be controlled in ways thatdisperse the sound outward in a wide-angled pattern (through the use of a convexsurface) or focus them on a specific point (through the use of a concave surface).Other surface shapes, on the other hand, can reflect sound back at various otherangles. For example, a 90º corner will reflect sound back in the same directionas its incident source (a fact that accounts for the additive acoustic buildups atvarious frequencies at or near a wall-to-corner or corner-to-floor intersection).

The all-time winner of the “avoid this at all possible cost” award goes toconstructions that include opposing parallel walls in its design. Such conditionsgive rise to a phenomenon known as standing waves. Standing waves (alsoknown as room modes) occur when sound is reflected off of parallel surfacesand travels back on its own path, thereby causing phase differences to interferewith a room’s amplitude response (Figure 3.20a). Room modes are expressedas integer multiples of the length, width and depth of the room and indicatewhich multiple is being referred to for a particular reflection.

Walking around a room with moderate to severe mode problems produces thesensation of increasing and/or decreasing volume levels at various frequenciesthroughout the area. These perceived volume changes are due to amplitude(phase) cancellations and reinforcements of the combined reflected waveformsat the listener’s position. The distance between parallel surfaces and the signal’swavelength determines the nodal points that can potentially cause sharp peaksor dips at various points in the response curve (up to or beyond 19 dB) at theaffected fundamental frequency (or frequencies) and upper harmonic intervals(Figure 3.20b). This condition exists not only for opposing parallel walls butalso for all parallel surfaces (such as between the floor and ceiling or betweentwo reflective flats). From this discussion, it’s obvious that the most effectiveway to prevent standing waves is to construct walls, boundaries and ceilingsthat are nonparallel.

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Primary Factors94

FIGURE 3.20 Standing waves within aroom. (a) Reflective parallelsurfaces can potentiallycancel and reinforcefrequencies within theaudible spectrum, causingchanges in its response. (b) The reflective, parallelwalls create an unduenumber of standing waves,which occur at variousfrequency intervals (f1, f2, f3,f4, and so on).

If the room in question is rectangular or if further sound-wave dispersion isdesired, diffusers can be attached to the wall and/or ceiling boundaries to helpbreak up standing waves. Diffusers (Figure 3.21) are acoustical boundaries thatreflect the sound wave back at various angles that are wider than the originalincident angle (thereby breaking up the energy-destructive standing waves). Inaddition, the use of both nonparallel and diffusion wall construction can reduceextreme, recurring reflections and smooth out the reverberation characteristicsof a room by building more complex acoustical pathways.

FIGURE 3.21 Diffuser examples: (a)SpaceArray sound diffusers.(Courtesy of pArtScience,www.partscience.com); (b) open-ended view of aPrimacousticTM Razorbladequadratic diffuser. (Courtesy of PrimacousticStudio Acoustics,www.primacoustic.com); (c) Art Diffusor sounddiffusers Models F, C & E.(Courtesy of acousticsfirst,www.acousticsfirst.com);(d) home-made woodendiffuser.

Flutter echo (also called slap echo) is a condition that occurs when parallel bound -aries are spaced far enough apart that the listener is able to discern a numberof discrete echoes. Flutter echo often produces a “boingy,” hollow sound thatgreatly affects a room’s sound character as well as its frequency response. Alarger room (which might contain delayed echo paths of 50 m/sec or more)

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can have its echoes spaced far enough apart in time that the discrete reflectionsproduce echoes that can actually interfere with the intelligibility of the directsound. This will often result in a jumble of noise, and in these cases, a properapplication of absorption and acoustic dispersion becomes critical.

When speaking of reflections within a studio control room, one long-helddesign concept relates to the concept of designing the room such that the rearof the room is largely reflective and diffuse in nature (acoustically “live”), whilethe front of the room is largely or partially absorptive (acoustically “dead”).This philosophy (Figure 3.22) argues for the fact that the rear of the room shouldbe largely reflective providing for a balanced and diffuse environment that canhelp reinforce positive reflections which can add acoustic “life” to the mixexperience (Figure 3.23). The front of the room would tend more toward theabsorptive side in a way that reduces standing-waves, flutter reflections andreflections from the rear of the speakers that would interfere with the overallresponse of the room.


FIGURE 3.22 Control-room layoutshowing the live end towardthe back of the room andthe dead end (absorption)toward the front of theroom.

FIGURE 3.23 Placing bookshelves alongthe rear wall and putting“stuff” on them can provideboth diffusion and a placefor lots of general storagefor things other than thenon-diffuse surfaces ofbooks.Co

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Primary Factors96

ABSORPTION

Another factor that often has a marked effect on an acoustic space involves theuse of surface materials and designs that can absorb unwanted sounds (eitheracross the entire audible band or at specific frequencies). The absorption ofacoustic energy is, effectively, the inverse of reflection (Figure 3.24). Wheneversound strikes a material, the amount of acoustic energy that’s absorbed relativeto the amount that’s reflected can be expressed as a simple ratio known as thematerial’s absorption coefficient. For a given material, this can be represented as:

A = Ia/Ir

where Ia is the sound level (in dB) that is absorbed by the surface (oftendissipated in the form of physical heat), and Ir is the sound level (in dB) thatis reflected back from the surface.

It’s important to realize that no two rooms will be

acoustically the same or will necessarily offer the

same design challenges. The one constant is that

careful planning, solid design and ingenuity are the

foundation of any good-sounding room. You should

also keep in mind that numerous studio design and

commercial acoustical product firms are available

that offer assistance for both large and small

projects. Getting professional advice can be a good

thing.

FIGURE 3.24 Absorption occurs whenonly a portion of the incidentacoustic energy is reflectedback from a material’ssurface.

The factor (1 – a) is a value that represents the amount of reflected sound. Thismakes the coefficient a decimal percentage value between 0 and 1. If we saythat a surface material has an absorption coefficient of 0.25, we’re actually sayingthat the material absorbs 25% of the original acoustic energy and reflects 75%of the total sound energy at that frequency. A sample listing of these coefficientsis provided in Table 3.2.

To determine the total amount of absorption that’s obtained by the sum of allthe absorbers within a total volume area, it’s necessary to calculate the averageabsorption coefficient for all of the surfaces together. The average absorptioncoefficient (Aave) of a room or area can be expressed as:

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Aave = s1a1 + s2a2 + . . . snan/S

where s1, s2, . . ., sn are the individual surface areas; a1, a2, . . ., an are the individualabsorption coefficients of the individual surface areas, and S is the total squaresurface area.

On the subject of absorption, one common misconception is that the use oflarge amounts of sound-deadening materials will reduce room reflections andtherefore make a room sound “good”. In fact, the overuse of absorption willoften have the effect of reducing high frequencies, creating a skewed roomresponse that is dull and bass-heavy, as well as reducing constructive roomreflections that are important to a properly designed room. In fact, with regard

Coefficients (Hz)

Material 125 250 500 1000 2000 4000

Brick, unglazed 0.03 0.03 0.03 0.04 0.05 0.07

Carpet (heavy, on concrete) 0.02 0.06 0.14 0.37 0.60 0.65

Carpet (with latex backing, on 0.03 0.04 0.11 0.17 0.24 0.3540-oz hair-felt or foam rubber)

Concrete or terrazzo 0.01 0.01 0.015 0.02 0.02 0.02

Wood 0.15 0.11 0.10 0.07 0.06 0.07

Glass, large heavy plate 0.18 0.06 0.04 0.03 0.02 0.02

Glass, ordinary window 0.35 0.25 0.18 0.12 0.07 0.04

Gypsum board nailed to 2 x 4 0.013 0.015 0.02 0.03 0.04 0.05studs on 16-inch centers

Plywood (3/8 inch) 0.28 0.22 0.17 0.09 0.10 0.11

Air (sabins/1000 ft3) — — — — 2.3 7.2

Audience seated in upholstered 0.08 0.27 0.39 0.34 0.48 0.63seats

Concrete block, coarse 0.36 0.44 0.31 0.29 0.39 0.25

Light velour (10 oz/yd2 in 0.29 0.10 0.05 0.04 0.07 0.09contact with wall)

Plaster, gypsum or lime (smooth 0.44 0.54 0.60 0.62 0.58 0.50finish on tile or brick)

Wooden pews 0.57 0.61 0.75 0.86 0.91 0.86

Chairs, metal or wooden, seats 0.15 0.19 0.22 0.39 0.38 0.30unoccupied

Note: These coefficients were obtained by measurements in the laboratories of the Acoustical Materials Association. Coefficients forother materials may be obtained from Bulletin XXII of the association.

Table 3.2 Absorption Coefficients for Various Materials

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Primary Factors98

to the balance between reflection, diffusion and absorption, many designersagree that a balance of 25% absorption and 25% diffuse reflections is a goodratio that can help preserve the “life” of a room, while reducing unwantedbuildups.

High-Frequency Absorption

The absorption of high frequencies is accomplished through the use of denseporous materials, such as fiberglass, Rockwool, dense fabric and carpeting. Thesematerials generally exhibit high absorption values at higher frequencies, whichcan be used to control room reflections in a frequency-dependent manner.Specially designed foam and acoustical treatments are also commerciallyavailable that can be attached easily to recording studio, production room orcontrol room walls as a means of taming multiple room reflections and/ordampening high-frequency reflections.

In addition to buying commercial absorbers, it’s very possible to put your handyshop tools to work by building your own cost-effective absorber panels (of anyshape, depth and style). One straightforward way of making them is by usingRockwool as the basic ingredient for your homemade absorber:

1. Measure the dimensions that you’ll need to build your absorbers. Buy1” × 4” fir boards that add up to your required dimensions (often, thehardware store will even cut them to suit your needs). You might alsowant to buy and measure your Rockwool bats at the same time (this mighthelp you with determining your overall dimensions).

2. Lay the boards out on your workbench or protected table and drill pilotholes to the top and bottom frame edges, then using a 2” sheetrock orother type of screw, screw the frames together.

3. Make your measurements for the amount of fabric that you’ll want tostretch over the entire surface and around the edges, so that they stretcharound the newly made box. The fabric can be of practically any type, buta nice, inexpensive fabric of your favorite color works well.

4. It always helps to iron the fabric, before mounting it, just to get thewrinkles out.

5. Before attaching the fabric, you might want to see how the Rockwool fitsinto each frame. If all’s ok, then begin carefully attaching the fabric to theframe with a heavy-duty staple gun, taking care that the fabric is tight,straight and looks good.

6. Once the fabric is attached and the Rockwool is inserted, it’s ready to hangin your control room/studio wall.

When done right, these absorbers (Figure 3.25) can look professional and fityour specific needs at a fraction of their commercial equivalents, sometimeswith better results.

High-Frequency Absorption

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FIGURE 3.25 Homemade absorber panel:(a) showing fabric that’s tobe stretched over a woodenframe; (b) once made, theRockwool is placed insidethe frame (which can be ofany size or form), it can behung on the wall, loweredfrom the ceiling or placed ina corner.

Low-Frequency Absorption

As shown in Table 3.2, materials that are absorptive in the high frequency rangeoften provide little resistance to the low-frequency end of the spectrum (andvice versa). This occurs because low frequencies are best damped by pliablematerials, meaning that low-frequency energy is absorbed by the material’sability to bend and flex with the incident waveform (Figure 3.26). Rooms thathaven’t been built to the shape and dimensions to properly handle the low end may need to be controlled in order to reduce the room’s resonancefrequencies.

FIGURE 3.26 Low-frequency absorption.(a) A carefully designedsurface that can be “bent”by oncoming sound wavescan be used to absorb low frequencies. (b) PrimacousticTM

Polyfuser, a combinationdiffuser and bass trap.(Courtesy of PrimacousticStudio Acoustics,www.primacoustic.com)

Another absorber type can be used to reduce low-frequency buildup at specificfrequencies (and their multiples) within a room. This type of attenuation device(known as a bass trap) is available in a number of design types:

n Quarter-wavelength trap

n Pressure-zone trap

n Functional trap

n Active trap

Low-Frequency Absorption

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Primary Factors100

The quarter-wavelength trap: The quarter-wavelength bass trap (Figure 3.27) is anenclosure with a depth that’s one-fourth the wavelength of the offendingfrequency’s fundamental frequency and is often built into the rear facing wall,ceiling or floor structure and covered by a metal grating to allow foot traffic.The physics behind the absorption of a calculated frequency (and many of theharmonics that fall above it) rests in the fact that the pressure component of asound wave will be at its maximum at the rear boundary of the trap when thewave’s velocity component is at a minimum. At the mouth of the bass trap(which is at a one-fourth wavelength distance from this rear boundary), theoverall acoustic pressure will be at its lowest, while the velocity component(molecular movement) will be at its highest potential. Because the wave’smotion (force) is greatest at the trap’s opening, much of the signal can beabsorbed by placing an absorptive material at that opening point. A low-densityfiberglass lining can also be placed inside the trap to increase absorption(especially at harmonic intervals of the calculated fundamental).

Pressure zone trap: The pressure-zone bass trap absorber (Figure 3.28) works onthe principle that sound pressure is doubled at large boundary points that areat 90º angles (such as walls and ceilings). By placing highly absorptive materialat a boundary point (or points, in the case of a corner/ceiling intersection), thebuilt-up pressure can be partially absorbed.

FIGURE 3.27 A quarter-wavelength basstrap: (a) physical conceptdesign; (b) sound is largelyabsorbed as heat, since theparticle velocity (motion) isgreatest at the trap’squarter-wavelengthopening.

FIGURE 3.28 Realtrap MegaTraps andabsorption curve. (Courtesyof RealTraps, LLC,www.realtraps.com)

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Functional trap: Originally created in the 1950s by Harry F. Olson (formerdirector of RCA Labs), the functional bass trap (Figure 3.29a) uses a materialgenerally formed into a tube or half-tube structure that is rigidly supported soas to reduce structural vibrations. By placing these devices into corners, roomboundaries or in a freestanding spot, a large portion of the undesired bassbuildup frequencies can be absorbed. By placing a reflective surface over theportion of the trap that faces into the room, frequencies above 400 Hz can bedispersed back into the room or focal point.

Active trap: An active bass trap system (Figure 3.29b) makes use of a microphone,low-frequency driver and a fast acting, band-limited amplifier to effectivelycreate an inverse pressure wave that electronically “absorbs” low-end frequencies.Such a unit is actually capable of creating an effective area of absorption thatis up to 40 times greater than its actual size.

ROOM REFLECTIONS AND ACOUSTICREVERBERATIONAnother criterion for studio design is the need for a desirable room ambienceand intelligibility, which is often contradictory to the need for good acousticseparation between instruments and their pickup. Each of these factors isgoverned by the careful control and tuning of the reverberation constants withinthe studio over the frequency spectrum.

Reverberation (reverb) is the persistence of a signal (in the form of reflected waveswithin an acoustic space) that continues after the original sound has ceased.The effect of these closely spaced and random multiple echoes give us perceptiblecues as to the size, density and nature of an acoustic space. Reverb also addsto the perceived warmth and spatial depth of recorded sound and plays anextremely important role in the perceived enhancement of music.

As was stated in the latter part of Chapter 2, the reverberated signal itself canbe broken down into three components:


FIGURE 3.29 Pressure zone bass trapexamples. (a) A functionalbass trap can be placed in acorner to prevent bassbuildup. (b) The PSI AudioAVAA C20 low-frequencyactive acoustic absorber.(Courtesy of PSI Audio,www.psiaudio.com)

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Room Reflections and Acoustic Reverberation102

n Direct sound

n Early reflection

n Reverb

The direct signal is made up of the original, incident sound that travels fromthe source to the listener. Early reflections consist of the first few reflections thatare projected to the listener off of major boundaries within an acoustic space.These reflections generally give the listener subconscious cues as to the size ofthe room. (It should be noted that strong reflections off of large, nearby surfacescan potentially have detrimental cancellation effects that can degrade a room’ssound and frequency response at the listening position.) The last set of signalreflections makes up the actual reverberation characteristic. These signals arecomposed of random reflections that travel from boundary to boundary in aroom and are so closely spaced that the brain can’t discern the individualreflections. When combined, they are perceived as a single decaying signal.

Technically, reverb is considered to be the time that’s required for a sound todie away to a millionth of its original intensity (resulting in a decrease overtime of 60 dB), as shown by the following formula:

RT60 = V × 0.049/AS

where RT is the reverberation time (in sec), V is the volume of the enclosure(in ft3), A is the average absorption coefficient of the enclosure, and S is thetotal surface area (in ft2). As you can see from this equation, reverberation timeis directly proportional to two major factors: the volume of the room and the absorption coefficients of the studio surfaces. A large environment with a relatively low absorption coefficient (such as a large cathedral) will have arelatively long RT60 decay time, whereas a small studio (which might incorporatea heavy amount of absorption) will have a very short RT60.

The style of music and the room application will often determine the optimumRT60 for an acoustical environment. Reverb times can range from 0.25 sec ina smaller absorptive recording studio environment to 1.6 sec or more in a largermusic or scoring studio. In certain designs, the RT60 of a room can be alteredto fit the desired application by using movable panels or louvers or by placingcarpets in a room. Other designs might separate a studio into sections that exhibitdifferent reverb constants. One side of the studio (or separate iso-room) mightbe relatively non-reflective or dead, whereas another section or room could bemuch more acoustically live. The more reflective, live section is often used tobring certain instruments that rely heavily on room reflections and reverb, suchas strings or an acoustic guitar, to “life.” The recording of any number of instru -ments (including drums and percussion) can also greatly benefit from a well-designed acoustically live environment.

Isolation between different instruments and their pickups is extremely importantin the studio environment. If leakage isn’t controlled, the room’s effectivenessbecomes severely limited over a range of applications. The studio designs of

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the 1970s and 1980s brought about the rise of the “sound sucker” era in studiodesign. During this time, the absorption coefficient of many rooms was raisedalmost to an anechoic (no reverb) condition. With the advent of the musicstyles of the 1990s and a return to the respectability of live studio acoustics,modern studio and control-room designs have begun to increase in size and“liveness” (with a corresponding increase in the studio’s RT60). This hasreintroduced the buying public to the thick, live-sounding music production ofearlier decades, when studios were larger structures that were more attuned tocapturing the overall acoustics of a recorded instrument or ensemble.

Acoustic Echo ChambersAnother physical studio design that was used extensively in the past (before theinvention of artificial effects devices) for re-creating room reverberation is theacoustic echo chamber. A traditional echo chamber is an isolated room that hashighly reflective surfaces into which speakers and microphones are placed.

The speakers are fed from an effects send, while the mic’s reverberant pickupis fed back into the mix via an input strip of effects return. By using one ormore directional mics that have been pointed away from the room’s speakers,the direct sound pickup can be minimized. Movable partitions also can be usedto vary the room’s decay time. When properly designed, acoustic echo chambershave a very natural sound quality to them. The disadvantage is that they takeup space and require isolation from external sounds; thus, size and cost oftenmake it unfeasible to build a new echo chamber, especially those that can matchthe caliber and quality of high-end digital reverb devices.

An echo chamber doesn’t have to be an expensive, built-from-the-ground-updesign. Actually, a temporary chamber can be made from a wide range ofavailable acoustic spaces to pepper your next project with a bit of “acousticspice.” For example:

n An ambient-sounding chamber can be built by placing a Blumlein (crossedfigure-8) pair or spaced stereo pair of mics in the main studio space andfeeding a send to the studio playback monitors.

n A speaker/mic setup could be placed in an empty garage (as could a guitaramp/mic, for that matter).

n An empty stairwell often makes an excellent chamber.

n Any vocalist could tell you what’ll happen if you place a singer or guitarspeaker/mic setup in the shower.

From the above, it’s easy to see that ingenuity and experimentation are oftenthe name of the makeshift echo/reverb game. In fact, there’s nothing that saysthat the chamber has to be a real-time effect—for example, you could play backa song’s effects track from a laptop DAW into a church’s acoustic space andrecord the space to stereo tracks on the DAW, where they can be later placedinto the mix. The limitless experimental options are totally up to you!


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chapter 3 studio acoustics francis group and design

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